Optimum reactive power compensation methodology to minimize system overvoltage conditions

Abstract

Sri Lankan Power system has experienced power frequency over voltages at steady state conditions predominantly at New Anuradhapura, New Chilaw and Chunnakam Grid Sub Stations. New Anuradhapura being connected to the lengthiest 220kV transmission lines from Kothmale (163km) and New Chilaw being connected to the Lakvijaya Power Station, which accounts to the highest capacity of national generation contribution and Chunnakam having long distance radial connection are the root causes for the issue. Currently the network overvoltages are mainly monitored at 220kV level due to sensitivity of the protection schemes implemented on the 220kV network equipment. Eg v/f, overvoltage protection, but all network equipments are vulnerable to overvoltage conditions despite their operation voltage level. In 27th September 2015, the most destructive event in terms of overvoltage occurred in the Sri Lankan power system initiating with tripping of Lakvijaya Gen 03 and ultimately causing a blackout. Post failure studies concluded with stressing out lack of reactive power compensation for overvoltage scenarios in present network topology. In power system, the reactive power compensation is important for system voltage profile. This is also helpful to power factor improvement and loss reduction. This study illustrates effectiveness of dynamic stability with integration of variable shunt reactors and static var compensators to the existing network topology, further studies are carried out to assess the effectiveness of disconnecting selected circuits to minimize overvoltage problem.